Technology now exists enabling switched voice and data communications over a single telephone connection. Switched voice and data communication is the process of temporarily blocking a telephone conversation during a call, sending data over the same connection, and then immediately returning to the conversation. A switched voice and data communication involves two modes of operation: voice mode where voice data is transferred between callers, and data mode where, for example, a binary data file is transferred between each caller's computer.
Combining voice and data communication in a single phone call opens the door to improved communication opportunities and a range of software applications to support such communication. Using switched voice and data communication, computer data such as text or graphics may be transferred and viewed by participants in a phone call as they converse on the phone. For instance, callers can discuss the same spread sheet file over the phone as they view it on their computer screens. Documents may be sent to and displayed on each caller's computer screen or screen phone during a call.
A communication device such as a fax or data modem used to transfer data over the telephone network must be modified or specifically built to support such switched voice and data communication. A communication device having this capability contains data circuit terminating equipment (DCE) to support time-multiplexed voice and data communications. The DCE generally includes a telephone network interface, a data terminal equipment (DTE) interface, and a local telephone interface. Linking the DCE to a telephone line, the telephone network interface couples the DCE to a general switched telephone network (GSTN). The telephone network interface is typically an analog telephone line connected to telephone network switch. The DTE interface couples the DCE to a data terminal device such as a personal computer (PC) for communicating commands and data to the DCE. Finally, the local telephone interface couples the DCE to a telephone for interactive voice communication.
A variety of communication devices may be equipped with switched voice and data communication capability. A DCE may be incorporated into communication devices such as modems, specialized telephones, and automated messaging systems. The DCE may be incorporated into a modem that is linked as follows: 1) to a local telephone through the local telephone interface, 2) to a PC through the DTE interface, and 3) to the GSTN through the telephone network interface. The DCE may also be incorporated into specialty phones such as a screen phone, in which case the local telephone interface may be implemented internally. A screen phone may not require a DTE interface if it has local data storage capability and the ability to display information. As another example, the DCE may be incorporated into a Voice Response Unit (VRU). A VRU is a device used in automated messaging. When incorporated into a VRU, the DCE can be used to transfer graphical information to accompany the computer generated voice messages of the VRU.
A communication device such as a modem equipped with switched voice-data capability operates as follows. When in voice mode, the modem supports standard interactive voice communication and acts as a monitor, looking for events that trigger a change to data mode. The modem monitors the voice communication connection and the data connection for specific events and changes its mode appropriately in response. When one person wants to send data to the other person on a call, the sending modem temporarily mutes the handset and sends a signal directing the receiving modem to switch to data mode. When the receiving modem receives the signal, it mutes the handset and prepares to receive data. After transferring the data, both modems unmute their handsets and normal conversation ensues.
To transfer files such as spread sheets or word processing documents, the computers of the respective participants in a the call act as DTEs, transferring commands and data to the DCE in a sending and receiving modem coupled to the respective computers, Through the sending modem, the sending computer transfers data from an application program to the receiving modem. The receiving modem then transfers this data to an application program in the receiving computer in response to commands issued by the computer. In this manner, the participants in the phone call can view the same data on their computer terminals while they discuss it over the phone.
Though switched voice communication can enhance interactivity between remote users of application programs, existing technology does not support simultaneous communication among more than one application program on each end of a telephone call. Only one application program can communicate with a modem at a time. This is a significant drawback because it prevents participants in a switched voice and data call from transferring data between more than one application program at once.
This drawback of existing switched voice and data technology arises from a limitation in the design supporting the communication. Current systems use a command set that fails to support communication among more than one application program. In a switched voice and data communication, the DTE such as a PC issues commands to the DCE such as a modem to control the transfer of data over the telephone line. In current systems, these control commands are standard AT commands based upon extensions to the TIA/EIA 602 and TIA/EIA 615 AT commands. These commands merely allow a single application to transfer data or to listen for a call at one time. The commands do not support transferring data to or from several applications at the same time.